Articles containing wood surfaces, such as furniture and cabinets, are often coated with one or more coatings. To provide color to such surfaces, toners and stains containing dyes and/or pigments are often used. Other surface layers, such as sealers and topcoats, may be used alone or in addition to such coloring layers. Typically, a sealer is applied either directly over the wood surface if no coloring layers are present, or, if a toner and/or stain is used, directly over such layers. A topcoat, if used, is typically applied over the sealer layer.
Coating compositions that are radiation curable are often desired, particularly for wood finish applications. Radiation curable coatings, such as those cured by exposure to ultraviolet (“UV”) radiation, are often desirable in wood finish applications because of the heat sensitivity of wood, which often makes certain thermosetting coatings undesirable. Acrylated resins are radiation curable and are often used in wood finish coatings.
Coatings that are essentially solvent-free are often desired because solvents, particularly organic solvents, can be costly, hazardous, and environmentally unfriendly. The presence of significant amounts of organic solvents in spray-applied coatings may be particularly undesirable for health and environmental reasons. Coatings that contain water or organic solvents can also be inefficient and costly, because these diluents must typically be evaporated from the coating before curing is complete.
Sprayable coatings are also often desired. Sprayability is often particularly desirable when the article to be coated is irregularly shaped, since it can be difficult to effectively coat such articles by other methods, such as roll coating. A sprayable coating is a coating that can be applied uniformly by atomization through a device, such as a spray gun, and is a function of the rheology profile of the coating. Generally, a coating composition with a viscosity of 2 to 300 cps at 25° C. (77° F.) is considered to be sprayable. Historically, solvents, such as water or organic solvents, have been required to attain such viscosities in radiation curable coatings. More recently, however, reactive diluents, such as relatively low molecular weight acrylate monomers, especially monofunctional acrylate monomers, have been used to achieve sprayability.
Historically, sealers and topcoats have been applied to wood surfaces by spray or roll on application of the coating to horizontally oriented wood substrates that is arranged on a conveyer system. An example of such a system is depicted in U.S. Pat. No. 6,746,535. In such an arrangement, the coating is deposited on one side of the article and then cured. Thereafter, if it is necessary to coat the other side of the article, the article is flipped and the process is repeated. As is apparent, such a process can be cumbersome.
As a result, it would be desirable to provide improved methods for coating substrates utilizing recyclable, substantially 100% solids, radiation curable coating compositions.